(1) Field of the Invention
This invention relates to sealed, through partition terminals for electrochemical cells, and more particularly to such terminals for lead-acid batteries.
(2) Description of Related Art
A typical terminal seal design consists of a brass terminal encapsulated in a lead terminal, elastomer coating, gasket, an inner top with an orifice and counterbore to accept the terminal and gasket, a mechanical fastener (push nut) and epoxy (see for example U.S. Pat. No. 5,380,603 to Hooke).
A gasket is strategically placed between the lead terminal which is coated with a protective elastomer and the counter bore of the inner top orifice. The gasket provides an acid tight seal when compressed and held in a compressed state with the combination of the terminal, the inner top and the mechanical fastener. The brass terminal has an outside diameter (O.D.) that provides a locking means with the mechanical fastener and maintenance free connection to the battery for the end user.
The epoxy is applied to encapsulate the mechanical fastener and to provide tamper resistance. The epoxy is color coated to distinguish polarity.
The elastomer coating such as CHEMLOK, (Lord Corporation, Elastomer Products Division), has manufacturing and environmental disadvantages. These materials are typically one-part or two-part polyurethane elastomers, formed from suitable isocyanate and active hydrogen supplying monomers or blocked polymers. Polysilane-containing elastomers, such as polysilane-containing urethane elastomers are typically used as sealing enhancing coatings.
The materials are difficult to dispense due to their required low viscosity and very short working time. The one-part formulas have a very limited shelf life therefore two-part systems are used to extend the same. This change adds to the dispensing and mixing difficulties due to a nonstandard mixing ratio (12:88 parts). A thirty minute cure time is required to allow the solvents used in the elastomer formulas to evaporate. The solvents used as diluents in the elastomer coatings promote attack of various engineering plastic resins and require proper ventilation when used.
The gasket is compressed axially between the lead and the shoulder of the cover orifice. The forces required to compress the gasket exceed the forces of the lead terminal therefore an external force needs to be applied to the terminal until the mechanical fastener is applied. This makes the machinery expensive, difficult to maintain and may result in production inconsistencies.
Epoxy is difficult to dispense and mix accurately. Variation in application technique results in the formation of air bubbles, cure rate and time fluctuation and product cleanliness. A one hour cure time is necessary due to product flow requirements. The cured material is designed to resist attack from any stray acid.